Thrombin Is a Potent Inducer of Connective Tissue Growth Factor Production via Proteolytic Activation of Protease-activated Receptor-1

Abstract

The coagulation protease thrombin plays a critical role in hemostasis and exerts pro-inflammatory and profibrotic effects via proteolytic activation of the major thrombin receptor, protease-activated receptor-1 (PAR-1). Connective tissue growth factor (CTGF) is a novel fibroblast mitogen and also promotes extracellular matrix protein production. It is selectively induced by transforming growth factor ␤ (TGF-␤) and is thought to be the autocrine agent responsible for mediating its pro-fibrotic effects. CTGF is up-regulated during tissue repair and in fibrotic conditions associated with activation of the coagulation cascade. We therefore hypothesized that coagulation proteases promote the production of CTGF by cells at sites of tissue injury. To begin to address this hypothesis, we assessed the effect of coagulation proteases on fibroblast CTGF expression in vitro, and we show that thrombin, at physiological concentrations, up-regulated CTGF mRNA levels 5-fold relative to base line (p < 0.01) in fetal fibroblasts and 7-fold in primary adult fibroblasts (p < 0.01). These effects were cycloheximide-insensitive and were not blocked with a pan-specific TGF-␤-neutralizing antibody. They were further paralleled by a concomitant increase in CTGF protein production and could be mimicked with selective PAR-1 agonists. In addition, fibroblasts derived from PAR-1 knockout mice were unresponsive to thrombin but responded normally to TGF-␤ 1 . Finally, factor Xa, which is responsible for activating prothrombin during blood coagulation, exerted similar stimulatory effects. We propose that coagulation proteases and PAR-1 may play a role in promoting connective tissue formation during normal tissue repair and the development of fibrosis by up-regulating fibroblast CTGF expression.

Protease-Activated Receptor-2 Expression in IgA Nephropathy

“…Coagulation cascade activation is a prominent feature of both acute and chronic inflammatory processes. Several reports support the hypothesis of a key role for coagulation factors in the pathogenesis of tissue fibrosis, particularly within the kidney (8,(27)(28)(29)(30). Interestingly, earlier works suggested that FXa, the enzymatically active constituent of the prothrombinase complex, triggers complex pathways involved in the regulation of cellular growth (31,32).…”

Glutathione S-Transferase Mu2 Suppresses Cancer Cell Metastasis in Non–Small Cell Lung Cancer

“…Regulators such as VEGF, S1P, and hypoxia-inducible factor (HIF)-1a have been reported to induce CCN2 production in different cells (26)(27)(28). CCN2 is also upregulated by other fibrogenetic cytokines including angiotension II, endothelin 1, and thrombin (29)(30)(31). On the other hand, epigenetic silencing by hypermethylation of the CCN2 promoter leads to a loss of CCN2 function, which may be a causative factor in the carcinogenesis of ovarian cancer (32).…”

PAR1 antagonism protects against experimental liver fibrosis. Role of proteinase receptors in stellate cell activation

“…8 -10 In addition to endogenous proteases, PARs can be selectively activated by short agonistic peptides (PAR-AP) that cor-respond to the tethered ligand exposed after PAR 1 and PAR 2 cleavage. 9,10 Studies with these agonists, as well as with PAR 1 -deficient mice, have led to the conclusion that PAR 1 is the major receptor responsible for mediating most of the proinflammatory and profibrotic effects 17 of thrombin.…”

“…18 -24 Thrombin might be mechanistically involved in regulating hepatic fibrogenesis. 5,17 Even though thrombin expression is increased in cirrhotic patients 5 and exposure of HSCs to thrombin triggers a number of effector functions, including proliferation, contraction, and collagen synthesis, 21,22 the functional relevance of PAR 1 in modulating HSC activity and collagen deposition in vivo is unknown. Fig.…”